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A reconstructionputs the in situ bones back into their in vivo places.

A restorationimagines the bones and soft tissues that are missing from the data. Adding scaled elements from a sister taxon is usually the best way to handle a restoration as we await further data from the field.

Figure 1. Tulerpeton restored based on the bauplan of Silvanerpeton and to the same scale.

We looked atTulerpeton, the Upper Devonian taxon known chiefly from its limbs, earlier. I reconstructed the limbs several ways, but did not attempt a restoration. Here (Fig. 1) that oversight is remedied based on the bauplan of Viséan sister, Silvanerpeton, also nesting at or near the base of the Reptilia (only amnion-layered eggs determine reptile status).

Among the overlapping elements,in Tulerpeton the pectoral girdle and forelimbs are larger. An extra digit is present laterally.

A large gamut phylogenetic analysis,like the large reptile tree (LRT, 1036 taxa, subset Fig. 2) should be able to find problems with smaller, more focused studies (Fig. 1) simply by virtue of its larger gamut. That one factor minimizes taxon exclusion issues, one of the biggest problems facing today’s vertebrate cladists. To that end, today we’ll take a look at the cladogram of Huttenlocker et al. 2013 (Fig. 1), which focuses on basal tetrapod (pre-reptile and microsaur) relationships.

Figure 1. Basal tetrapod cladogram in Huttenlocker et al. 2013. This looks like a lot of taxa, but it is not. Color added here. Light green are taxa that nest within lepospondyli in the LRT. Taxa not colored, except for Acanthostega, are not tested in the LRT. Note how many taxa are missing here compared to the LRT. That gives the false impression that lepospondyls arose from Eryops and Greererpeton, which are unrelated basal taxa in the LRT. Limnoscelis nests deep within the Reptilia, so should not even be included here.

Not every taxon tested by Huttenlocker et al.(Fig. 1) appears in the LRT (Fig. 2). And vice versa. The light green areas are all in one clade, the Lepospondyli, on the LRT. Note they form a large majority of taxa in the Huttenlocker et al. cladogram. That some nest with basalmost tetrapods and temnospondyls appears to be yet another case of taxon exclusion by Huttenlocker. Nearly all the taxa are lepospondyls with just two clades, Eryops and the Reptilomorpha, breaking them up. Had they added more Eryops kin and more Reptilomorpha, plus some missing basal lepospondyls, like Utegenia (widely considered another reptilomorh/seymouriamorph), and some even more basal sarcopterygian/ basal tetrapods, as they appear in the LRT, perhaps the tree topologies would start to look more alike.

FIgure 2. Subset of the LRT has a larger gamut of taxa. Here lepospondyls nest together when more basal tetrapods are added to the taxon list than are present in figure 1. Lavender taxa are ‘Recumbirostro” in the Huttenlocker et al. tree, but are microsaurs here. Limnoscelis nests deeper within the Reptilia.

Ariekanerpeton sigalovi (Ivakhnenko 1981, Laurin 1996; PIN 2079-1; Early Permian ~280 mya, 25cm in length; Fig. 1) is represented by more than 900 specimens. None are considered fully mature due to their juvenile-type paired neural arches disarticulated from the pleurocentra. Is it possible that this genus retained juvenile traits into adulthood?

No dermal scales are present. Lateral lines are present only on aquatic larvae (with limbs). The large ones traversed arid landscapes. IMHO, that makes them adults with neotony.

I did not find
the ventrally expanded quadratojugal applied to the reconstruction by Laurin 1996 (Fig. 1). Rather the quadratojugal appears to have been rather straight.

Figure 1. Ariekanerpeton is known from over 900 specimens, none of them apparent adults. It nests at the base of the Seymouriamorpha, close to stem Lissamphibia + stem Reptilia. See how even a little dash of color clarifies these line illustrations?

In the LRT
(large reptile tree, 1035 taxa) Ariekanerpeton nests at the base of the Seymouriamorpha, between Eucritta (near the base of the reptilomorphs) and Utegenia (at the base of the lepospondyls) + Bystrowiella (at the base of the stem reptiles). This taxon, therefore, is transitional between several clades. We’ve already seen that neotony attends the origin of major clades, and Ariekanerpeton fits that model 3 times!

Figure 2. Discosauricus is also known from many dozen specimens, none of whom have been adjudged to be adult. This taxon nests closer to Seymouria.

Discosauricus (Fig. 2) is similar in many waysto Ariekanerpeton, but nests on the other side of Kotlassia, closer to Seymouria.

Discosauriscus austriacus (Makowsky 1876; Klembara 1997, Klembara and Bartik 1999; Early Permian, 250 mya; Fig. 2) is also known from several hundred specimens from larvae to subadult stages. The palate was closed only in the largest specimens. Manual and pedal digits 4 had five phalanges, as in Seymouria and one more than in Ariekanerpeton. The ilium had a robust posterior process and a small anterior process.

The morphology of the atlas-axis complex is similar to that in Seymouria sanjuanensis. The neural arches start to swell slightly in specimens of late larval stage; they are completely swollen immediately after metamorphosis. The six caudal ribs should have been lateral in orientation (Fig. 2 boxed), pointing posteriorly, rather than ventrally as Klembara and Bartik illustrated them.

No digit 6 in basal seymouriamorphsTulerpeton, a basal amniote/reptile has 6 digits (Fig. 3). The absence of manual and pedal digit 6 in basal seymouriamorpha further isolates Tulerpeton, suggesting the extra digit appeared as a derived autapomorphy, rather than a primitive character putatively relating Tulerpeton to fish-like taxa, such as Acanthostega, which has 8 digits. Let’s not forget…

On the other hand…we have not yet found any Late Devonian seymouriamorphs or reptilomorphs. And they should be there. So the number of digits in those hypothetical specimens could be six and that trait should remain an open question at present.

ReferencesIvakhenko MF 1981. Dscosauriidae from the Permain of Tadrzhikistan. Paleontological Journal 1981:90-102.Klembara J 1997. The cranial anatomy of Discosauriscus Kuhn, a
seymouriamorph tetrapod from the Lower Permian of the Boskovice Furrow (Czech Republic). Philosophical Transactions of the Royal Society of London, Series B. 352: 257–302.Klembara J and Bartik I 1999. The postcranial skeleton of Discosauriscus Kuhn, a seymouriamorph tetrapod from the Lower Permian of the Boskovice Furrow (Czech Republic). Transactions of the Royal Society of Edinburgh: Earth Sciences 90(4):287–316.Laurin M 1996. A reevaluation of Ariekanerpeton, a lower Permian seymouriamorph (Vertebrata: Seymouriamorpha) from Tadzhikistan. Journal of Vertebrate Paleontology 16(4):653–665.

Traditional paleontology has given us a picture of a more or less simple ladder of stem tetrapod evolution that had its key moment when an Ichthyostega-like taxon first crawled out on dry land. Then, according to the widely accepted paradigm, certain lineages returned to the water while others ventured forth onto higher and drier environs.

By contrast,
The large reptile tree (LRT, 1033 taxa) documents a bushier conquest of land, occurring in at least seven Devonian waves until the beachhead was secured by our reptile ancestors.

Dr. Jennifer Clack and her team have shown us that fish/amphibians can have limbs (Acanthostega and Ichthyostega) and not be interested in leaving the water. That comes later and later and, well, seven times all together.

Figure 1. Colosteus relatives according to the LRT scaled to a common skull length. Their sizes actually vary quite a bit, as noted by the different scale bars. Only Pholidogaster and Colosteus are taxa in common with traditional colosteid lists.

The first wave:
simple small fins to simple small limbsArising from lobe-fin fish with one nostril migrating to the inside of the mouth, like Osteolepis, the much larger collosteid, Pholidogaster, had small limbs with toes. The smaller, but equally scaly and eel-like Colosteus, reduced those limbs to vestiges, showing they were not that important for getting around underwater in that wriggly clade. Neither shows signs of ever leaving the water and phylogenetically neither led to the crawling land tetrapods. However, like the living peppered moray eel (Gymnothorax pictus, Graham, Purkis and Harris 2009) in search of crabs, these taxa might have made the first landfall without limbs. See terrestrial moray eel videohere.

Figure 2. Greererpeton reduced to a blueprint of body parts. Here there may be one extra phalanx on pedal digit 5 and one missing on pedal digit 2 compared to sister taxa. So an alternate is shown with that repair. The skulls at left are juveniles.

The second wave:
fins to limbs on long flattened bottom feedersFully limbed Greererpeton and Trimerorhachis were derived from finny flat taxa like Panderichthys and Tiktaalik. Both Greererpeton and Trimerorhachis were likewise flat- and long-bodied aquatic forms that seem unlikely to have been able to support themselves without the natural buoyancy of water. Their descendants in the LRT likewise look like they were more comfortable lounging underwater like living hellbenders (genus Cryptobranchus. According to Wikipedia: “The hellbender has working lungs, but gill slits are often retained, although only immature specimens have true gills; the hellbender absorbs oxygen from the water through capillaries of its side frills.” Only rarely do hellbenders leave the water, perhaps to climb on low pond rocks. If the Greererpeton clade was similar, this would have been the second meager and impermanent conquest of the land. And they would not have gone too far from the pond.

Figure 3. Pederpes is a basal taxon in the Whatcheeria + Crassigyrinus clade.

The third wave: the Pederpes/Eryops clade experimented with overlapping ribs.
Arising from shorter Ossinodus and Acanthostega, a clade that included Pederpes, Ventastega, Baphetes and Eryops arose. This clade looks quite capable of conquering the land for the third time. Their overlapping ribs helped support their short backbone, for the first time lifting their belies off the substrate when doing so, matching Middle Devonian tracks. Some clade members, like Crassigyrinus (with its vestigial limbs) and Saharastega (with its flattened skull) appear to have opted for a return to a watery environment. And who could blame them? In any case, their big lumbering bodies were not well adapted to clambering over dry obstacles, like rocks and plants, that made terrestrial locomotion more difficult. And the biggest best food was still in the water. No doubt limbs helped many of them find new ponds and swamps when they felt the urge to do so, like living crocs. And they probably left the water AFTER some of the smaller and more able taxa listed below.

Figure 4. Proterogyrinus had a substantial neck.

The fourth wave:a longer neck and a smaller head gave us Proterogyrinus.Ariising from fully aquatic fish/amphibians with overlapping ribs, like Ichthyostega, basal reptilomorphs, like low-slung, lumbering Proterogyrinus took the first steps toward more of a land-living life. The nostrils shifted forward, but were still tiny, at first. Bur the ribs were slender without any overlap. Perhaps this signaled improvements in lung power. Larger nostrils appeared in more devoted air breathers, like Eoherpeton and Anthracosaurus. All these taxa were still rather large and lumbering and so were probably more at home in the water.

Figure 5. Eucritta in situ and reconstructed. Note the large pes in green.

The fifth wave:goes small, gets longer legs and gives us Seymouria.Eucritta is the first of the small amphibians with longer limbs relative to trunk length. This clade also arises from Ichthyostega-like ancestors. One descendant clade begins with a several long-bodied, short-legged salamander-like taxa. Discosauriscus is one of these. It begins life in water, but grows up to prefer dry land. Seymouria is the culmination of this clade.

Figure 6. Utegenia nests as a sister to Diplovertebron.

The sixth wave:gives us salamanders and frogs.Still tied to the water for reproduction and early growth with gills, this clade arises from the seymouriamorph/lepospondyl Utegenia, a short-legged, flat-bodied aquatic taxon. That plesiomorphic taxon gives rise to legless Acherontiscus and kin including modern caecilians. Reptile-mimic microsaurs, like Tuditanus arise from this clade. So do modern salamanders, like Andrias and long-legged, short bodied frogs, like Rana. Their marriage to or divorce from water varies across a wide spectrum in living taxa.

Figure 7. Various stem amniotes (reptiles) that precede Tulerpeton in the LRT. So these taxa likely radiated in the Late Devonian. And taxa like Acanthostega and Ichthyostega are late-survivors of earlier radiations documented by the earlier trackways.

The seventh wave:gives us the amniotic egg and the reptiles that laid them.No one should have ever said you have to look like a typical reptile to lay an amnion-covered egg. And if they did, they were not guided by a large gamut phylogenetic analysis. This clade become fully divorced from needing water for reproduction, but basal members still liked the high humidity and wet substrate of the swamp. Arising from basalmost seymouriamorphs like Ariekanerpeton, stem reptiles included Bystrowiellaand Silvanerpeton. These were small agile taxa with relatively long legs that would have had their genesis in the Late Devonian. Their first appearance in the fossil record was much later. The development of the amnion-enclosed embryo may have taken millions of years. The first phylogenetic reptiles appear in the form of amphibian-like Gephyrostegus and Tulerpetonin the Late Devonian, which still had six fingers and scales, but these lacked layers typically found in more fish-like taxa.

So the conquest of the landby stem and basal tetrapods appears to have occurred seven times, according to the LRT, from distinct clades that were more or less ready to do so and in different ways. And, of course, odd extant fish, like the Peppered moray eel (wave 8) and the mudskipper, (wave 9) and maybe even snakes from stem sea snakes (wave 10) continue this tradition. What will THEY eventually evolve into, given enough time?

Narrow-gauge older tracks from Zalchemie
(387 million years ago) also had a shorter stride on a longer torso, matching tetrapods without long lateral limbs, but with short stubs or limbs, like Tiktaalik appearing 12 million years later.

Figure 2. Chronology of Devonian stem tetrapod taxa and trackways. Frame one shows traditional tree without tracks. Frame two extends ghost lineages to consider the tracks as evidence of undiscovered fossils. Fossils represent rare discoveries typically long after major radiations to millions of individuals, increasing the odds of their being found.

The problem isthe wider tracks come from an era in which Tiktaalik-like taxa are known as fossils, some 25 million years too soon based on fossil taxa like Ichthyostega, (Fig. 3).

Figure 3. Best Devonian Valentia track with various overlays.

The solution isfossils of all sorts can be discovered close to the genesis of a clade, but are more likely to be discovered close to the maximum radiation (in terms of numbers of individuals), increasing the odds for preservation and discovery. Applying logic here, the skeletons must be appearing near the maximum radiation while the ichnites must be appearing near the genesis of the clade. But wait, there’s more:

Figure 5. Various stem amniotes (reptiles) that precede Tulerpeton in the LRT. So these taxa likely radiated in the Late Devonian. And taxa like Acanthostega and Ichthyostega are late-survivors of earlier radiations documented by the earlier trackways.

The taxa listed above(Fig. 5) all precede Latest Devonian Tulerpeton in the large reptile tree (LRT, 1027 taxa), though their first appearance in the fossil record occurs much later in every case. That must mean the genesis of the various radiations that produced these taxa must have occurred in the Late Devonian. Currently that’s heresy. But that’s where the current evidence leads us. At present these clues tell us where to look in the geological column and what to look for.

And for all you future paleontologists:
there’s a great paper waiting for the next person or team to find these pre-Tulerpeton taxa in Late Devonian strata. Based on the stress to living things that occurred during the Latest Devonian extinction event, perhaps these taxa radiated quickly and widely.

Figure 1. Lethiscus stocki skull, drawing from Pardo et al. 2017 and colorized here. Note the loss of the postfrontal and the large orbit. Pardo et al. nest this taxon between Acanthostega and Pederpes in figure 3. There is very little that is plesiomorphic about this long-bodied legless or virtually legless taxon. Thus it should nest as a derived taxon, not a basal plesiomorphic one.

Lethiscus is indeed very old (Middle Viséan)but several reptiles are almost as old and Tulerpeton, a basal amniote, comes from the even older Late Devonian. So the radiation of small burrowing and walking tetrapods from shallow water waders must have occurred even earlier and Tulerpeton is actually the oldest crown tetrapod.

Figure 3. Pardo et al. cladogram nesting Lethiscus between vertebrates with fins and vertebrates with fingers. They also nest microsaurs as amniotes (reptiles), resurrecting an old idea not supported in the LRT. Actually not much of this topology is supported by the LRT.

Pardo et al. nested Lethicus
between Acanthostega (Fig. 4) and Pederpes (Fig. 3) using a matrix that was heavily weighted toward brain case traits. Ophiderpeton and Oestocephalus (Fig. 2) were not included in their taxon list, though the clade is mentioned in the text: “Overall, the skull morphology demonstrates underlying similarities with the morphologies of both phlegethontiid and oestocephalid aïstopods of the Carboniferous and Permian periods.” So I’m concerned here about taxon exclusion. No other basal tetrapods share a lateral temporal fenestra or share more cranial traits than do Lethiscus, Ophiderpeton, Oestocephalus and Rileymillerus. All bones are identified here as they are in Pardo et al. so bone ID is not at issue. I can’t comment on the Pardo team’s braincase traits because so few are examined in the LRT. Dr. Pardo said they chose taxa in which the brain case traits were well known and excluded others.

Figure 4. Acanthostega is basal to Lethiscus in the Partdo et al. tree.

Pardo et al. consideredthe barely perceptible notch between the tabular and squamosal in Lethiscus (Fig. 1) to be a “spiracular notch” despite its tiny size. I think they were reaching beyond reason in that regard. They also note: “The supratemporal bone is an elongate structure that forms most of the dorsal margin of the temporal fenestra, and is prevented from contacting the posterior process of the postorbital bone by a lateral flange of the parietal bone.” The only other taxon in the LRT that shares this morphology is Oestocephalus, Together they nest within the Lepospondyli (Fig. 3) in the LRT. I think it is inexcusable that Pardo et al. excluded Ophiderpeton and Oestocephalus.

Figure 4. Subset of the LRT with the addition of Lethiscus as a sister to Oestocephalus, far from the transition between fins and feet. Here the microsaurs are not derived from basal reptiles

Summarizing,
Pardo et al. report, “The braincase and its dermal investing bones [of Lethiscus] are strongly indicative of a very basal position among stem tetrapods.” and “The aïstopod braincase was organized in a manner distinct from those of other lepospondyls but consistent with that seen in Devonian stem tetrapods.” It should also be noted that the skull, body and limbs were likewise distinct from those of other lepospondyls, yet they still nest with them in the LRT because no other included taxa (1018) share more traits. ‘Distinct’ doesn’t really cut it, in scientific terms. As I mentioned in an email to Dr. Pardo, it would have been valuable to show whatever bone in Lethiscus compared to its counterpart in Acanthostega and Oestocephalus if they really wanted to drive home a point. As it is, we casual to semi-professional readers are left guessing.

Pardo et al. references the clade Recumbirostra.Wikipedia lists a number of microsaurs in this clade with Microbrachis at its base, all within the order Microsauria within the subclass Leposondyli. Pardo et al. report, “Recumbirostrans and lysorophians are found to be amniotes, sister taxa to captorhinids and diapsids.” The LRT does not support this nesting. Pardo et al. also report, “This result is consistent with early understandings of microsaur relationships and also reflects historical difficulties in differentiating between recumbirostrans and early eureptiles.”Yes, but the later studies do not support that relationship. Those early understandings were shown to be misunderstandings that have been invalidated in the LRT and elsewhere, but now resurrected by Pardo et al.

Figure 5. A series of Phlegethontia skulls showing progressive lengthening of the premaxilla and other changes.

A side note:The recent addition of several basal tetrapod taxa has shifted the two Phlegethontia taxa (Fig.5) away from Colosteus to nest with Lethiscus and Oestocephalus, their traditional aistopod relatives. That also removes an odd-bedfellow, tiny, slender taxon from a list of large robust stem tetrapods.

Yesterday Pardo et al. 2017
described two conspecific and incomplete amphibians in the lineage of caecilians, Chinlestegophis jerkinsi (DMNH 56658, DMNH 39033, Figs. 1, 3). These long-sought specimens were discovered in the late 1990s preserved in Late Triassic burrows.

This is really big news!Congratulations to the Pardo team!!

From the abstract:“Here, we report on a small amphibian from the Upper Triassic of Colorado, United States, with a mélange of caecilian synapomorphies and general lissamphibian plesiomorphies. We evaluated its relationships by designing an inclusive phylogenetic analysis that broadly incorporates definitive members of the modern lissamphibian orders and a diversity of extinct temnospondyl amphibians, including stereospondyls. Stem caecilian morphology reveals a previously unrecognized stepwise acquisition of typical caecilian cranial apomorphies during the Triassic. A major implication is that many Paleozoic total group lissamphibians (i.e., higher temnospondyls, including the stereospondyl subclade) fall within crown Lissamphibia, which must have originated before 315 million years ago.”

The diagnosis:“Small stereospondyl with a combination of brachyopoid and caecilian characteristics.” Stereospondyls were generally large, flat-skulled aquatic taxa that had simplified and rather weak vertebrae in which the intercentrum was topped by a neural arch and the pleurocentrum was reduced to absent. According to Wikipedia, “All lepospondyls have simple, spool-shaped vertebrae that did not ossify from cartilage, but rather grew as bony cylinders around the notochord.”

This is the opposite of
Reptilomorphs, in which the pleurocentra are large and the intercentra are smaller. Reptilomorphs generally were smaller and better adapted to terrestrial environments.

In the LRT traditional stereospondyls
(Fig. 5, pink) are mid-sized basalmost tetrapods, aquatic with a weak backbone because they are not far from fish with fins. Temnospondyls have stronger limbs and stronger backbones (Fig. 5, yellow), but typically remain large and aquatic.

Reptilomorphs
(Fig. 5, orange) tend to be smaller with stronger limbs and vertebrae and reduce their dependence on water. Both lepospondyls (including living amphibians) and reptiles arise from this clade in the LRT.

Few microsaurs
were included in the Pardo et al study (Fig. 4) and the topology of their tree is very different from the present topology. Caecilians nest with lepospondyl microsaurs in the large reptile tree (LRT, 2014).

In addition
several skull bones are identified differently here (Fig. 1) than in the Pardo et al. study (Fig. 3).Pardo et al. identify an otic notch (that hole in the temporal region). Here that appears to be the space left open after the supratemporal has popped out during taphonomy. The supraorbital bones are all re-identified and both the lacrimal and quadratojugal are now listed in the present identification of bones. Based on conversations with Pardo and others, bone identification on several taxa may be the cause of the differing tree topologies.

Figure 1. GIF movie showing the two skulls of Chinlestegophis from Pardo et al. 2017 with DGS colors applied to both along with a revised set of bone label based on phylogenetic bracketing among the previously excluded microsaurs close to caecilians.

First step: Learn about RileymillerusAs usual, I knew nothing about this taxon earlier this week. Now, according to the LRT Rileymillerus nests with Oestocephalus and Ophiderpeton, two other long-bodied microsaurs with round cross-section skulls, not included in the Pardo et all study. The apparent loss or lack of bones in the temporal region may be homologous with the lateral temporal fenestra in Ophiderpeton. That’s a rare trait among basal tetrapods.

Figure 2. Rileymillerus from Bolt and Chatterjee 2000 with colors applied. Note the lack of bone on both sides of the temples in this specimen, as in Ophiderpeton. The color (DGS) identify of the bones here is not in complete accord with Bolt and Chatterjee. As you can see, the skull has many cracks, which makes finding the sutures that much more difficult.

UnfortunatelyPardo et al. excluded most of the taxa that the LRT found were most closely related to the clade Chinlestephos + (caecilians + lysorophians) That includes Microbrachis and the rest of the microsaurs. They had good reason for doing so (see below).

Figure 3. Chinlestegophis diagram. Drawings produced by Pardo et al. At left bones colored as they labeled them. At right same bone colors rearranged to fit the new interpretation. See figure 1. The lateral temporal fenestra is interpreted here as the spot on the skull that once held the supratemporal. No related taxa have a lateral temporal fenestra in either cladogram.

The Pardo et al. skull bone labels
differ from the present interpretation (Fig. 3). Even with such massive dissonance, Pardo et al. and the LRT both nest Chinlestegophis with caecilians and not far from Rileymillerus.

How can such a thing happen??
I can’t answer that at present. It’s frankly surprising.

Figure 4. Pardo et al. cladogram nesting caecilians as ultra-derived temnospondyls. Taxa also present in the LRT are highlighted to show the general mixup of taxa that the LRT separates.

The drifting of the postorbitalIn most tetrapods the postorbital is one of the circumorbital bones. In caecilians and their relatives the postfrontal takes over that spot and the postorbital drifts posteriorly, still lateral to the parietal. This observation may be one of the issues attending circumorbital and temporal bone identification arguments in this clade.

Figure 5. Basal tetrapod subset of the LRT. This cladogram includes microsaurs. When given the opportunity to nest with microsaurs, caecilians do so.

In their Supplemental InfoPardo et al. added the traits for Chinlestegophis to the dataset of Maddin et al. 2012 (who earlier described Jurassic Eocaecilia) and found Chinlestegophis nested with Rileymillerus, close to the stem frog Micromelerpeton and strong-legged Acheloma all far from the caecilians and all derived from a sister to giant Eryops. This study did include microsaurs. Lots of them! Other mismatches include nesting the large reptile Limnoscelis between Seymouriaand tiny Utaherpeton and Microbrachis, taxa that share few traits with each other in the LRT. Numerous other morphological mismatches also occur In Maddin et al. Evidently no one is using scaled reconstructions in their analyses as a final check on these mismatches. In the LRT caecilians nest with similar long-bodied, tiny-limbed taxa, which some claim is due to convergence. On a similar note, the LRT lumped and separated snakes from amphisbaenids while other trees failed to do this. So perhaps convergence is not the reason here when dealing with burrowing amphibians.

Figure 6. Maddin et al. cladogram featuring only two temnospondyls from the LRT. Here Chinlestegophis does not nest with caecilians and Rileymllerus nests far from Oestocephalus.

A note from Jason Pardorestates that the Maddin et al. study “found no close relationship between Eocaecilia and lepospondyls nor did we find a close relationship between Chinlestegophis and those taxa.”

All three cladograms
share few major branches in common. As everyone knows by now, the major branches are the more difficult ones to determine. And, if we can’t agree on the identify of the skull bones, of specimens, the tree topologies will have a hard time finding consensus.

Diphyletic (two separate ancestries) with apodans (=caecilians) within the lepospondyls andsalamandersandfrogswithin the temnospondyli.”

Figure 9. Skull of Microbrachis in several views. Here is where the postorbital leaves the orbit margin and drifts posteriorly. Compare to Chinlestegophis above.

So… even the experts have not come to a consensuson basal tetrapod topologies. The LRT agrees that the lissamphibia are monophyletic within the lepospondyli, matching option #2 above. There are many aspects of caecilians that need to be interpreted in light of their phylogeny. And we’re not coming to a consensus on that. Earlier we looked at the fusion of the cheek bones in caecilians here with the extant taxon Dermophis.

ReferencesBolt JR and Chatterjee S 2000. A New Temnospondyl Amphibian from the Late Triassic of Texas. Journal of Paleontology 74(4):670-683.Maddin HC, Jenkins FA, Jr, Anderson JS 2012. The braincase of Eocaecilia micro podia (Lissamphibia, Gymnophiona) and the origin of Caecilians. PLoS One 7:e50743.Pardo JD, Small BJ and Huttenlocker AK. 2017, Stem caecilian from the Triassic of Colorado sheds light on the origins of Lissamphibia. PNAS: 7 pp. www.pnas.org/cgi/doi/10.1073/pnas.1706752114